Abstract

The optical constants of unintentionally doped cubic GaN grown on GaAs(001) have been measured at 300 K using spectral ellipsometry in the range of 1.5–5.0 eV. The spectra display a structure associated with the critical point at (direct gap) and some contribution mainly coming from the critical point. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden–Muñoz modeldielectric function [M. Muñoz et al., J. Appl. Phys. 92, 5878 (2002)]. This model is based on the electronic energy-band structure near critical points plus excitonic and band-to-band Coulomb-enhancement effects at and the doublet. In addition to evaluating the energy of the critical point, the binding energy of the two-dimensional exciton related to the critical point was estimated using the effective theory. The line shape of the imaginary part of the cubic-GaN dielectric function shows excitonic effects at room temperature not withstanding that the exciton was not resolved.